Thermoplastic elastomers are rubbery materials which can be thermoformed by techniques generally associated with thermoplastic resins. They normally contain elastomeric domains and crystalline or partially crystalline thermoplastic domains. The elastomeric phase lends rubbery properties, while the relatively hard thermoplastic phase provides strength below the melting point of the thermoplastic elastomer and processability above the melting point. Examples of elastomers used in thermoplastic elastomers are ethylene/propylene rubber (EPR), ethylene/propylene/diene rubber (EPDM), acrylonitrile-butadiene rubber (NBR), and natural rubber (NR). These elastomers may or may not be crosslinked. Examples of thermoplastic resins used in thermoplastic elastomers are polypropylene, high density polyethylene, low density polyethylene, polystyrene, and polyamides. When the elastomeric phase is crosslinked, the method of crosslinking must be selective to the elastomer so as to avoid crosslinking the thermoplastic phase, and thus retain processability. Typical crosslinking methods reported in the literature are based on sulfur, peroxide, phenolics, and ionic curing, all of which have serious drawbacks during manufacture or with respect to the end use of the resulting products.
The process of preparing thermoplastic elastomers by crosslinking an elastomer in the presence of a thermoplastic polymer is known as "dynamic curing". One technique of classical dynamic curing is described in a paper by Coran and Patel published in Rubber Chemistry and Technology, volume 53, 1980, pages 141 to 150, with reference to EFPDM/polypropylene based thermoplastic elastomers. Unfortunately, dynamic curing, as currently practiced, suffers from the generation of low molecular weight species, the use of toxic, noxious, or explosive reagents; and modification, e.g., viscosity changes, of the thermoplastic polymer.